U(VI) sorption by CTAB/Bent–MOF-74 from various carbonate solutions
CTAB/Bent-MOF-74 was synthesized via hydrothermal method to investigate its U(VI) sorption in carbonate solutions. Generally, CTAB/Bent-MOF-74 (∼87.6 mg·g −1 ) showed better sorption capacity than CTAB/Bent-MOF-71 (∼64.2 mg·g −1 ) and CTAB/Bent-CS-35 (∼81.4 mg·g −1 ) in U(VI)-Cl coexist carbonate solutions when pH = 8.0, [NaHCO 3 ] =2 mmol·L −1 , [NaCl] =0.1 mol·L −1 and [U(VI)] =50 mg L −1 . The competitive sorption between HCO 3 − /CO 3 2− , OH − , halide ions and U(VI) complexes ions as well as the weakened electrostatic attraction decreased the composite's uranium sorption efficiency and capacity at high pH initial , NaHCO 3 , phosphate, Ca/Mg and halide ions concentrations. The pseudo-second-order kinetics and Langmuir models indicated a monolayer homogeneous chemisorption process. Besides, 0.1 mol·L −1 HCl shows the highest desorption efficiency among the selected desorbents, and the sorption rate is still high even after four times of desorption. In particular, the decreasing inhibitory capacity of the halide ions was on the order of I − , F − , Br − , Cl − . Characterization analyzes confirmed the good structural stability and Br anion exchange as well as the -OH/-COOH coordination and electrostatic attraction, which could be the predominant sorption mechanisms of U(VI) by CTAB/Bent-MOF-74. The results provided theoretical references for understanding the uranium sorption in natural uranium-containing water and designing potential uranium-extracting materials.
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